MOD = 10 ** 9 + 7
n = int(input())
a = list(map(int, input().split()))
t = 1
ans = 0
for i in range(n):
    t *= a[i]
    t %= MOD
    if i == n - 1:
        ans += t
    else:
        ans += t * 2 * pow(3, n - i - 2, MOD)
print(ans % MOD)